Rolling contact bearing steels and process for heat treating the same



A ril 28, 1964 D. v. GULLOTTI ETAL 3,131,056

ROLLING CONTACT BEARING STEELS AND PROCESS FOR HEAT TREATING THE SAME Filed April 20, 1962 3 Sheets-Sheet 3 ALLOY 7315 //Y ssco/vos l l l l l l I l l 2 4 e 8 l0 l2 l4 lb I8 20 27.

D/smnrcc 590M Quewcfleo Eva //y Sums/"m OFAIY //vc11 INVFNTORS J. S D 41y 1/ GUCLOTT/ BY Jomy L. HueLsy A rroewer United States Patent 3,131,056 RULLING OGNTACT BEARIYQ STEELS AND PROOESS FOR HEAT TREATING THE SAME Damian V. Guiiotti, Bayonne, John L. Hurley, Bloomfield,

and Herschel V. Beasiey, Short Hills, N.J., assignors to The International Nickel (lornpany, Inn, New York,

N.Y., a corporation of Delaware Filed Apr. 20, 1962, Ser. No. 189,133 8 Claim. ((11. 75-124) The present invention relates to alloy steels and, more particularly, to through-hardening low alloy rolling contact bearing steels of special composition characterized by a unique combination of metallurgical properties, to an improved process for heat treating the alloy steels and to ball and roller bearings and the like fabricated from such steels.

As is known to those skilled in the art, extremely high quality standards are exacted of steels used for ball and roller bearings. As indicated at page 121 of U.S.S. Carilloy Steels, published by the US. Steel Corp. in 1948, bearings are utilized in a tremendous number of applications ranging from small precision instruments employing bearings weighing a fraction of an ounce to battleship turrets containing roller bearing assemblies which weigh tons. A survey of the literature reflects that there are relatively few through-hardening low alloy steels for applications of high Rockwell hardness (Rc), e.g., Rc62 and greater, possessing high hardenability and high hardness combined with ease of processing. This is not to be unexpected since the hardness of such steels is primarily a function of carbon content. To achieve satisfactory hardness for ball and roller bearings manufactured from through-hardening steels extremely high carbon contents, e.g., about 1% or more, have been necessary. Unfortunately, high carbon and high hardness are not normally those attributes conducive to achieving ease of carrying out the necessary processing operations. A distinct disadvantage or shortcoming of steels used heretofore has been the necessity of employing relatively high processing temperatures and/or relatively long treatment times as will be explained more fully herein.

A ball or roller bearing through-hardening alloy steel should, if possible, possess in combination the following characteristics:

(a) High hardness (b) High hardenability without quench cracking (0) Ability to oil quench to full hardness (d) Relatively low processing temperatures and short periods of heat treatment during spheroidizing annealing (e) Uniform annealed structure (f) Ease of machining as annealed These characteristics pertain to what might be considered as four major criteria in selecting a steel for bearing applications, to wit, hardenability, hardness, microstructure and cost.

White hardness can be viewed as simply the ability of a steel to resist plastic deformation, unless a Rockwell surface hardness of Rc62 and preferably at least R063 can be attained, the optimum requirements of the instant invention will not be met for ball and roller bearing manufacture. In connection with this aspect, a significant attribute of a steel for bearing applications should be its ability to oil quench (as distinct from water quench) to full hardness. Maximum surface hardness often can be achieved in many steels upon a water quench but not with an oil quench; however, the severity of the former is causative of cracks and/ or distortion. The ultimate would be a steel which develops, as a practical matter, substantially its highest hardness upon an oil quench.

Apart from hardness and hardenability, the annealed microstructure of an alloy steel for bearing applications is a most important criterion. Microstructure to a large measure governs or determines the ease with which the steel may be machined prior to hardening. A more than adequate microstructure would be one comprised of a relatively uniform spheroidite distribution in ferrite and manifesting a maximum hardness of about 220 Brinell and advantageously not over about 200 Brinell. This spheroidite distribution is accomplished through the application of a spheroidization anneal heat treatment cycle.

Various spheroidization anneal heat treatment cycles have been proposed and are presently used commercially. Of the prior art through-hardening steels used for ball or roller bearings, AISI 52100 (a steel containing about 0.95% to 1.1% carbon, 0.25% to 0.45% manganese, 0.2% to 0.35% silicon and 1.3% to 1.6% chromium, and on rare occasion molybdenum, vanadium or aluminum) has been so extensively employed that it has become a standard. However, an apparent comparative disadvantage of this steel is the relatively lengthy period of time for heat treatment employed during the pheroidization anneal cycle. Alloy Digest, published by the Engineering Alloys Digest, Inc. of Upper Montclair, New Jersey, (SA-16) of 1954 sets forth the following heat treatment cycle for AISI 52100: (a) normalize, air cool from 16501700 F., (b) anneal, furnace cool from 1425- 1450 F., (c) spheroidize, slow cool at a rate of 5 F. per hour from a temperature at about the Acm point, i.e., about 1415 F, after an extended holding period at about the Acm temperature. Thereafter, the steel is quench hardened. Even if the cooling period of 5 F. per hour is only carried down to 1250 F., a period of about 33 hours is required simply to achieve a spheroidized structure. This is not only a lengthy processing time, but also contributes to increasing the cost of final product.

A further problem that has been encountered in bearing manufacture with respect to certain applications is the retention of austenite upon quenching from the austenitizing temperature subsequent to the spheroidization anneal treatment. Retained austenite is to be avoided since it can result in impairment of fatigue properties. In addition, when a bearing is in use and subjected to heavy loads (a specific application of the through-hardening bearing steels) the retained austenite tends to transform and thus distortion can occur necessitating replace ment of the bearing. Moreover, where present in substantial amounts, e.g., above 20%, low hardness results. This difliculty of austenite retention has arisen to some extent with AISI 52100 since under commercial conditions, austenite is almost invariably retained. Attendant this problem, bearing steels should be characterized by relatively high Ms temperatures since low Ms temperatures are conducive to quench cracking and/or distortion upon quenching. Put another way, if AISI 52100, for example, Were austenitized at a relatively high temperature, e.g., 1700 F. or 1800 F, considerable danger would be invited since a greater amount of carbon would be made available which would depress the Ms temperature and result in a greater amount of retained austenite. The fact that greater amounts of carbon are made available with higher austenitization of A181 52100 is reflected by the flattening out of its hardenability curve, i.e.,

horizontal line. It would be beneficial to provide a built- 3) in safety factor, i.e., to provide for the situation that if a relatively high austenitizing temperature, e.g., 1700 F., happened to be used, no adverse effects attributable to retained austenite would result. This would minimize the necessity of close processing control.

It has now been discovered that through-hardening low alloy roller contact bearing steels containing certain amounts of carbon, manganese, silicon, nickel, chromium and molybdenum can be provided such that when subjected to a special and improved heat treatment a highly satisfactory combination of properties and characteristics is attained. The high hardness, high hardenabiiity and ease of processing possessed by these special steels render them eminently suitable for ball and roller bearing applications.

it is an object of the present invention to provide ball or roller bearing steels which manifest a unique combination of metallurgical properties including high hardenability, high hardness and ease of processing, including a uniform annealed structure which is easily machinable and which can be oil quenched without the occurrence of detrimental distortion and/ or cracking.

Another object of the invention is to provide an improved heat treatment which when applied to the contemplated alloy steels affords a highly satisfactory combination of results.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURES 1 and 2 depict Jominy hardenability data with respect to various alloy steel compositions;

FIGURE 3 sets forth hardness data resulting from tests conducted in accordance with bearing industry practice;

FIGURE 4 reflects the results of machinability tests; and

FIGURE 5 represents hardenability curves for several alloy steels which were subjected to the spheroidize anneal treatment of the present invention and austenitized.

Generally speaking and in accordance with the instant invention, a highly satisfactory combination of characteristics are achieved with alloy steels of the following advantageous ranges: from 0.67% to about 0.8% carbon, from 0.3% to about 0.75% maganese, about 0.25% to about 0.4% silicon, from 0.75% to about 1% nickel, from 0.12% to about 0.4% chromium, about 0.1% to about 0.3% molybdenum and the balance essentially iron. Aluminum in amounts up to 0.5% is most advantageous to insure the attainment of a fine grain size consistent with commercial steel making practice.

Steels within the foregoing ranges when subjected to the special heat treatment described hereinafter afford a surface hardness of at least R062 and up to R066, a uniform annealed structure (a uniform dispersion of spheroidite in a matrix of ferrite) upon annealing and a Brinell hardness easily controllable to not greater than about 220, e.g., 185 to 200, in the spheroidized condition. Further, the steels are not only relatively easy to machine but can be cooled at a rate as high as 25 F. per hour during the spheroidization cycle and, thus, do not require long processing times or excessively high temperatures for heat treatment either for spheroidization or hardening. However, although high austenitizing temperatures are unnecessary, it is to be pointed out that these steels can be austenitized over a relatively wide temperature range without encountering adverse effects, i.e., the Ms temperature of these steels will not be lowered to a point where deleterious cracking or distortion upon quenching occurs. Thus, there is a built-in safety factor which obviates need of close processing control.

For continuously achieving optimum results, it is important that the foregoing compositional ranges be ob served. Carbon, for example, not only tends to decrease hardness and hardenability in amounts lower than set forth above, but carbon in amounts above 0.8% has been found to induce or cause a decrease in hardness. Manganese in amounts above the ranges hereinabove specified can promote quench cracking while amounts below 0.3% are conducive to inadequate hardenability. Sufiicient silicon should be present for deoxidation purposes but excessive amounts can contribute to quench cracking. While nickel contributes to hardenability and toughness, excessive amounts promote the retention of austenite. If too much chromium is employed, retention of austenite can be the result, but a sufficient amount, advantageously at least 0.12%, is necessary not only to promote hardenability but to accelerate the rate at which the steel spheroidizes on cooling. Molybdenum acts in a manner quite similar to chromium, i.e., promotes hardenability and speed-up of spheroidization rate.

Satisfactory results can also be achieved with alloy steels having the following broad range: 0.6% to 0.8% carbon, 0.3% to 0.8% manganese, silicon in an amount sufficient for deoxidation of the steels, e.g., 0.15%, up to 0.5%, 0.5% to 1.5% nickel, 0.1% to 0.45% chromium, 0.05% to 0.35% molybdenum, the balance being essentially iron. While acceptable results can be obtained with compositions within the foregoing broad range (but outside the advantageous range given hereinbefore), much more rigid control of the overall processing operations is required to obtain these results. For example, to meet the necessary requirements, it is unsatisfactory to use a low carbon content, e.g., 0.6%, together with amounts of the other elements on the low side. If a steel with a carbon content of say about 0.64% or 0.65% were employed, comparatively high austenitizing temperatures, e.g., 1600 F. to 1700 F. would have to be employed. In fact, a normalizing treatment might well have to be employed prior to austenitizing since a normalizing treatment can result in higher hardenability. Close control of temperature conditions and other processing operations would be needed, thereby requiring unnecessary supervision in the processing operations. However, it is an object of the invention to obviate any need of high processing temperatures and/or additional heat treatments and, thus, it is much more advantageous to utilize compositions falling within the ranges first given herein.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better appreciation of the advantages thereof, the following illustrative description and data are given:

EXAMPLE 1 Several alloy steels having compositions within the ranges set forth above together with an alloy steel (Alloy F) outside the scope of the invention were prepared and are identified in Table I.

Table I Element) Percent Acid Alloy $211.,

C Mn Si Ni Cr Mo 65 53 27 88 13 21 021 67 55 26 S9 13 21 024 i0 55 28 84 13 2 1 020 75 5S 31 86 13 19 015 78 43 25 90 13 21 057 96 44 23 89 13 18 032 1 Iron essentially the balance.

Alloys A through F were made in the following manner. Two melts were made in a high frequency induction furnace with silicon and aluminum being used for deoxidation purposes. Each melt was split into about 30 lb. ingots, pig-iron being added between pourings to vary the carbon content (alloys A, B, C and D of Table I). In addition, two other ingots were prepared, these being directed to higher carbon content levels (alloys E and F of Table I). All ingots were forged to 2% inch squares, one-half being retained as such with the remainder being hot-rolled to 1% inch rounds.

In accordance with standard practice, Jominy hardenability bars were prepared from the hotrolled rounds and tested for each of the alloys A through F, the only deviation from standard procedure being that flats 0.03 inch deep were ground on the bars instead of the usual 0.015 inch depth. This was done as one of many precautionary measures, i.e., to avoid inaccuracies which might result from possible decarburization. For these tests, alloys A through F were normalized at 1700 F., were austenitized at 1600 F. and were end-quenched in the Jorniny fixture after which the hardness was measured at the standard J distances of sixteenths of an inch from the quenched end. FIGURE 1 correlates the 1 distance to a Rockwell hardness of R063 for each of these alloy steels. FIGURE 2 graphically depicts the hardenability cooling curves for alloy D when normalized at 1700 F. and quenched from austenitizing temepratures of 1475 F., 1525 F., 1600 F. and 1700 F., respectively, the curves being typical of those for steels falling within the advantageous ranges set forth hereinbefore.

FIGURES 1 and 2 illustrate the excellent hardenability which is characteristic of alloy steels B, C, D and E. Alloy A (broad range) which contained 0.65% carbon exhibited less hardenability than alloys B through D. Alloy B which contained 0.67% carbon and was otherwise similar in composition to alloy A manifested much higher hardenability. Alloy F which is outside the scope of the invention shows a marked drop in hardenability although it contained the highest carbon content. It should be pointed out that the hardenability of alloy A might be raised to a satisfactory level if a much higher austenitizing temperature, e.g., 1700 F., were employed.

In addition to the foregoing, alloys A, B, C and D were also subjected to a test employed by the bearing industry, a test adapted to obtain traverse hardness data. These tests were conducted by machining the 2 /2 inch squares to 2 inch square blocks with a thickness of inch. The blocks were normalized at 1700 F., austenitized at the temperatures shown in FIGURE 3 and then oil quenched. The hardness traverses were conducted perpendicular to each other (depicted in FIGURE 3 by solid dots for one direction and circles for the other direction) on a 2 inch square face (along the center of the faces) that had been surface ground. To pass the requirements of this test the hardness must not fall below Rockwell C 63. As illustrated in FIGURE 3, this hardness was achieved for each alloy while using an oil quench; however, FIGURE 3 again illustrates that it is most advantageous to maintain the carbon content at least as high as 0.67% (alloy B). Alloy A (0.65% carbon) when austenitized at 1525 F. and 1600 F. exhibited less hardness at the center of the face of the blocks, i.e., a Rockwell hardness which at various points was less than Rc63. This data rather confirms the results of the Jcminy tests, i.e., alloys A and B are quite similar in composition but the higher carbon steel (0.67%) of alloy B manifested superior hardness. Higher austenitizing treatment (1700 F., FIG. 3) combined with the normalizing treatment enabled the required hardness level to be achieved in alloy A.

As indicated hereinbefore, processing the steels of the instant invention is accomplished with relative ease. In accordance with the invention, the spheroidization anneal cycle comprises holding at a temperature above the Ae temperature, and advantageously at least about 25 F. above the Ae temperature, for a period sufficient to form a fine uniform carbide dispersion in a matrix of austenite. This is important so that on cooling below the Ae temperature, the particles serve as nuclei for spheroidite rather than lamellar pearlite. The holding temperature advantageously does not exceed the Acm temperature and a holding temperature range of about 1365 F. to about 1390 F., e.g., 1375 F., for about one hour per inch of section is very suitable. The alloy steels are then cooled at a rate of up to 25 F. per hour until spheroidization is essentially complete. A cooling rate of 10 F. per hour has been found quite advantageous considering commercial steel making practice. Further, it has been found that the cooling cycle need not extend to a temperature below the range of 1250 F.

to 1200 F. Thus, the spheroidization kinetics of steels.

in accordance with the invention, particularly those with the aforementioned advantageous range, are quite rapid. For example, if the cooling operation in the heat treatment for spheroidizing AISI 52100 as given in the Alloy Digest is brought down to 1250 F. as are the steels contemplated herein, a period of 33 hours would be required as compared with from 5 hours to 12 /2 hours in accordance with the present invention. Subsequent to the cooling treatment the alloy steels are quenched from autenitizing temperature. Of course, it is, as mentioned herein, a feature of the invention that low processing temperatures can be employed and in accordance therewith an advantageous austenitizing temperature range is 1475 F. to 1600 F., a temperature of 1500 F. having been found very satisfactory. Temperatures above 1600 F. can be employed without particular benefit with respect to the advantageous range given herein. However, such higher temperatures do not create the difiiculties described with regard to AISI 52100 and thus a built-in safety factor is provided. Of course, austenitizing at above 1600 F., e.g., 1700 F. or higher, will be beneficial for those alloy steels within the broad range but outside the advantageous range described hereinbefore, particularly if coupled with a prior normalizing treatment.

The steels spheroidized in accordance with the invention are easily machined, a Brinell hardness of not more than 200 being readily achieved. Further, the hardness of such steels when austenitized at 1500 F. is at least equivalent, and actually better, than that of AISI 52100 commercially'hardened from 1540 F. Moreover, softening tests have shown that it takes at least 300 to 700 hours at 350 F. for hardness to drop from a Rockwell hardness R064 or R065 to Rc58. This is indicative that alloy steels used in accordance with the invention resist softening.

The spheroidization, machinability and hardness characteristics are illustrated by the following example EXAMPLE 2 A series of nine 30 lb. air-induction melts were made having compositions set forth in Table II.

Table 11 Alloy l 0 Mn Si Ni Cr M o 1 About 0.05% aluminum added, balance essentially iron.

The steels were homogenized at 2200" F. then forged and rolled at 1900 to 2000 F. to 1% inch rounds. The spheroidization anneal cycle applied consisted of holding at a temperature of 1375 F. for one hour and then cooling at a rate of 10 F., 25 F. or 50 F. per hour. Controlled cooling was halted at 1200 F., the power being discontinued to allow the natural cooling rate of the furnace to take over. The effect of the cooling rates in terms of carbide dispersion (measured by random traverses), Brinell hardness and microstructural constituents in the ferrite matrix is given in Table III for alloys 1 and I which are illustrative of the results obtained (these alloys representing the high side and low side analyses of composition).

1 Number of particles intersected per 4 inches of random linear traverse at 1000 diameters.

The 10 F./hr. cooling rate as reflected by the data in Table III is eminently satisfactory and even with the 25 F./hr. Cooling rate, the desired hardness level and microstructure were achieved. This illustrates that adherence to slow cooling rates, e.g., 5 F. per hour, is quite unnecessary. In connection with this aspect, alloy E was also removed from the annealing furnace at 1250" F. and at 800 F. and the structure examined. It was found that essentially identical structures and hardnesses were obtained at these temperatures in comparison with the structure obtained at 1200 F. Thus, it is not necessary to carry the cooling treatment of the spheroidization anneal cycle down to temperatures below 1250 F. to 1200" F. Thus, the furnace time saved by removal at 1250" F. rather than at 800 F. or even 1200 F. results in a substantial economy, i.e., reduction of annealing cost.

The machinability test comprised affixing a weight to a drill press in such manner that a constant load (30 lbs.) was applied to the drill bit and thus to the alloy steel specimens tested. Several specimens of the spheroidized alloy steels cooled at a rate of F. per hour and also an AISI 52100 specimen (cooled at a rate of 5 F. per hour) were held in a vise, the assembly being submerged in an oil-water lubricant emulsion. The time to drill a depth of 0.535 inch was used for comparison purposes. A constant drill speed was employed with a new drill bit being used for each test. In all instances the machinability, the results of which are given in FIG- URE 4, was very satisfactory. Generally less time was required to drill to the depth of 0.535 inch for alloy steels of the invention than for AISI 52100. The same test was also applied to specimens cooled at a rate of 25 F. per hour during the spheroidization cycle and the results compared favorably with AISI 52100 cooled at the rate of 5 F. per hour.

For the hardenability test, spheroidized annealed bar stock was machined into Jominy hardenability bars and flats 0.030 inch deep were ground 180 apart. The spheroidized specimens were quenched from an austeriitizing temperature of 1500 F. with Rockwell C readings being taken every one-sixteenth of an inch therealong. FIGURE 5 graphically represents the hardenability curves and includes hardenability data (dotted line curves and cross-hatching) for AISI 52100 quenched from an austenitizing temperature of 1540 F. Alloy M which is outside the invention and which contained 0.64% carbon and low manganese (0.19%) failed to exhibit the requisite hardness whereas all the other steels not only manifested satisfactory hardenability but in many cases, cg, alloys E, H, I and N, were characterized by higher hardenability than AISI 52100. When austenitized at a temperature higher than 1500 F., to Wit, 1550 F., hardenability was increased.

As those skilled in the art will readily appreciate, the Ae and Acm temperatures of the alloy steels of the present invention will vary to some extent from one specific composition to another. Generally, the Ae temperatures of the steels are of the order of about 1340 F. and the Acm temperatures are of the order of about 1410 F. Further, those skilled in the art will also appreciate that the holding period during the spheroidization anneal cycle may be varied. As mentioned hereinbefore, as holding period of about one hour per inch of thickness has been found to be quite satisfactory. Even with section thicknesses of less than one inch, the holding time should be at least one hour. Of course, longer periods may be employed, the important point being that the holding operation be conducted for a time sufiicicnt to form the fine uniform carbide dispersion in a matrix of austenite.

Since the through-hardening low alloy steels of the present invention and particularly the advantageous range thereof are characterized by a combination of properties including high hardenability and hardness, relatively short periods for spheroidize annealing, a uniform annealed structure which is also easily machinable and amenability to relatively low austenitizing temperature treatment, the steels are particularly adaptable as roller contact bearing steels for manufacture of ball and roller bearings and bearing races. Such characteristics also render the alloy steels suitable for use in applications requiring high wear resistance and good elasticity. The alloy steels, particularly those within the advantageous range, have desirably high Ms temperatures. No problem concerning retained austenite is encountered. For example, no detectable retained austcnite was found on X-ray analysis of alloy B of Table I which was normalized at 1700 F., austenitized at 1600 F. and oil quenched. However, alloy F showed a retained austenite content of about 38% upon X-ray examination, alloy F having been treated in the same manner as alloy B. In addition, alloy F exhibited surface cracks whereas no cracking occurred with regard to alloy B. Moreover, heat treatments such as normalizing are not required and the rapid kinetics of the sphcroidize anneal treatment is a particular advantage of the invention.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A process for heat treating through-hardening, low alloy rolling contact bearing steels which comprises holding an alloy steel consisting of from 0.67% to about 0.8% carbon, from 0.3% to about 0.75% manganese, silicon in an amount up to 0.4%. from 0.75% to about 1% nickel, from 0.12% to about 0.4% chromium, about 0.1% to about 0.3% molybdenum and the balance essentially iron at a temperature above its Ae temperature and below its Acm temperature for a period of at least about 1 hour to form a fine uniform carbide dispersion in a matrix of austenite and to provide upon cooling a condition where carbide particles serve as nuclei for spheroidite rather than lamellar pearlite, and cooling the alloy steel to a temperature of about 1250 F. to about 1200 F. at a rate of from about 10 F. to about 25 F. per hour to obtain a structure having a uniform sphcroidite distribution.

2. A process for heat treating a rolling contact bearing steel which comprises holding an alloy steel consisting of from 0.6% to 0.8% carbon, 0.3% to 0.8% manga nese, silicon in an amount up to 0.5%, 0.5% to 1.5% nickel, 0.1% to 0.45% chromium, 0.05% to 0.35% molybdenum, aluminum up to 0.5% and the balance essentially iron at a temperature above its Ae temperature and below its Acm temperature for a period of at least about 1 hour to form a fine uniform carbide dispersion in a matrix of austenite and to provide upon cooling a condition where carbide particles serve as nuclei for spheroidite rather than lamellar pearlite, and cooling the alloy steel to a temperature of about 1250 F. to about 1200 F. at a rate of from about 10 F. to about 25 F. per hour to obtain a structure having a uniform spheroidite distribution.

3. A heat treating process for providing a throughhardened, low alloy rolling contact bearing steel having high hardenability, a surface hardness of at least Rc62 and good resistance to softening which comprises holding an alloy steel consisting of from 0.67% to about 0.8% carbon, from 0.3% to about 0.75% manganese, silicon in an amount up to 0.4%, from 0.75 to about 1% nickel, from 0.12% to about 0.4% chromium, about 0.1% to about 0.3% molybdenum, aluminum in an amount up to 0.5 and the balance essentially iron at a temperature of at least about 25 F. above its Ae temperature for at least about one hour per inch of section to form a fine uniform carbide dispersion in a matrix of austenite and to provide upon cooling a condition where carbide particles serve as nuclei for spheroidite rather than lamellar pearlite, cooling the alloy steel to a temperature at least as low as about 1250 F. at a rate of from about F. to about 25 F. per hour to obtain a structure having a uniform spheroidite distribution and a hardness of not appreciably greater than about 220 Brinell, and thereafter quenching the said steel from an austenitizing temperature of about 1475 F. to about 1700 F.

4. A heat treating process for providing a throughhardened, low alloy rolling contact bearing steel having high hardenability, a surface hardness of at least Rc62 and good resistance to softening which comprises holding an alloy steel consisting of from 0.6% to 0.8% carbon, 0.3% to 0.8% manganese, silicon in an amount up to 0.5%, 0.5% to 1.5% nickel, 0.1% to 0.45% chromium, 0.05% to 0.35% molybdenum, aluminum up to 0.5 and the balance essentially iron at a temperature of at least about 25 F. above its Ae temperature for at least about one hour per inch of section to form a fine, uniform carbide dispersion in a matrix of austenite and to provide upon cooling a condition where carbide particles serve as nuclei for spheroidite rather than lamellar pearlite, cooling the alloy steel to a temperature at least as low as about 1250 F. at a rate of from about 10 F. to about 25 F. per hour to obtain a structure containing a uniform spheroidite distribution and a hardness of not appreciably greater than about 220 Brinell, and thereafter quench- 10 ing the said steel from an austenitizing temperature of about 1475 F. to about 1700 F.

5. A through-hardening, low alloy rolling contact bearing steel having a combination of characteristics including high hardenability, a surface hardness of at least Rc62, the ability to oil quench to such hardness, good resistance to softening and consisting of 0.67% to about 0.8% carbon, from 0.3% to about 0.75% manganese, silicon in an amount up to 0.4%, from 0.75% to about 1% nickel, from 0.12% to about 0.4% chromium, about 0.1% to about 0.3% molybdenum and the balance essentially iron, said alloy steel being further characterized by a spheroidized carbide microstructure when heat treated at a temperature above its Ae temperature and below its Acm temperature for a period of at least about one hour and cooling the alloy steel to a temperature at least as low as 1250 F. at a rate of from about 10 F. to about 25 F. per hour.

6. A rolling contact bearing member formed from the through-hardening low alloy steel set forth in claim 17.

7. A rolling contact bearing steel having high hardenability, a surface hardness of at least Rc62, the ability to oil quench to such hardness, good resistance to softening and consisting of 0.6% to about 0.8% carbon, 0.3% to 0.8% manganese, silicon in an amount up to 0.5%, 0.5% to 1.5% nickel, 0.1% to 0.45% chromium, 0.05% to 0.35% molybdenum, aluminum up to 0.5 and the balance essentially iron, said alloy steel being further characterized by a spheroidized carbide microstructure when heat treated at a temperature above its Ae temperature and below its Acm temperature for a period of at least about one hour and cooling the alloy steel to a temperature at least as low as 1250 F. at a rate of from about 10 F. to about 25 F. per hour.

8. A rolling contact bearing member formed from the alloy steel set forth in claim 7.

Herman Feb. 28, 1928 Turner May 31, 1960 

7. A ROLLING CONTACT BEARING STEEL HAVING HIGH HARDENABILITY, A SURFACE HARDNESS OF AT LEAST RC62, THE ABILITY TO OIL QUENCH TO SUCH HARDNESS, GOOD RESISTANCE TO SOFTENING AND CONSISTING OF 0.6% TO ABOUT 0.8% CARBON, 0.3% TO 0.8% MANGANESE, SILICON IN AN AMOUNT UP TO 0.5%, 0.5% TO 1.5% NICKEL, 0.1% TO 0.45% CHROMIUM, 0.05% TO 0.35% MOLYBDENUM, ALUMINUM UP TO 0.5% AND THE BALANCE ESSENTIALLY IRON, SAID ALLOY STEEL BEING FURTHER CHARACTERIZED BY A SPHEROIDIZED CARBIDE MICROSTRUCTURE WHEN 